In a magnetic recording method, an increase in the recording density causes the magnetic bit to be seriously susceptible to external temperature and other factors. This requires use of a recording medium having a greater coercive force. However, use of such a recording medium, in turn, increases the magnetic field required for recording. The maximum of the magnetic field generated by the recording head is determined by the saturation magnetic flux density. This value, however, has already come very close to the limit of material, and a drastic increase cannot be expected. A solution to this problem is proposed in a technique wherein magnetic weakening is caused by local heating at the time of recording, and recording is performed when the coercive force is reduced. After that, heating is suspended and natural cooling is performed, whereby the stability of the recorded magnetic bit is ensured. This proposed technique is referred to as a thermally assisted magnetic recording method.
In the thermally assisted magnetic recording method, the recording medium is preferably heated instantaneously. Further, a heating device is not allowed to be in contact with a recording medium. Thus, it is a common practice to use absorption of light for heating. The method of using light for heating is referred to as an optically assisted magnetic recording method. When the optically assisted method is used for extra high-density recording, the required diameter of the spot is about 20 nm. In the normal optical system, condensation of light cannot be performed to meet this requirement, because of the presence of a diffraction limit. Solutions to this problem can be found in the technique having been proposed, wherein the near field light, which is a non-propagation light, is utilized for heating (Patent Document 1). According to this technique, laser beam having an appropriate wavelength is condensed by an optical system, and is applied to a metal (called the plasmon probe) having a size of several tens of nanometers, whereby near field light is generated. This near field light is used for heating.
In another proposed technique (Patent Document 2), the material having a high refractive index is used to manufacture the plasmon probe for generating the near field light and the substrate for forming the plasmon probe (Patent Document 2). In still another proposed technique (Patent Document 3), a plasmon probe is formed in close proximity to the medium having a high refractive index such as silicon, gallium arsenide and germanium.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2005-116155
Patent Document 2: Japanese Unexamined Patent Application Publication No. 2003-114184
Patent Document 3: Japanese Unexamined Patent Application Publication No. 2004-28900